Photohelic Switch/Gages function as versatile, highly
repeatable pressure switches combined with a precise pressure gage
employing the time-proven Magnehelic gage design. The Photohelic
switch/gage measures and controls positive, negative or
differential pressures of air and compatible gases. Standard models
are rated to 25 psig (1.7 bar) with options to 35 (2.4) or 80 (5.5
bar) psig. Two phototransistor actuated, DPDT relays are included
for low/high limit control. Easy to adjust setpoint indicators are
controlled by knobs located on the gage face. Individual setpoint
deadband is one pointer width - less than 1% of full scale.
Setpoints can be interlocked to provide variable deadband - ideal
for control of fans, dampers, etc. Gage reading is continuous and
unaffected by switch operation, even during loss of electrical
power. Choose from full scale pressure ranges from a low up to
0-50"wc; single positive pressure to 6000 psig (413 bar).

In typical applications, these Dwyer switch/gages
control between high and low pressure set points. When pressure
changes, reaching either set point pressure, the infrared light to
the limiting phototransistor is cut off by the helix-driven light
shutter. The resulting phototransistor signal is electronically
amplified to actuate its DPDT slave relay and switching occurs.
Dead band between make and break is 1% of full scale or less - just
enough to assure positive, chatter-free operation.

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